1. Field of the Invention
The invention relates to the field of maintenance and repair of aeronautical parts, in particular of the blades of a turboshaft engine.
2. Description of the Related Art
A blade is understood to be a part having a surface capable of channelling an air flow in the turboshaft engine, wherein this part may be movable (rotor blade) or fixed (stator blade).
Conventionally, in the course of a maintenance operation of a turboshaft engine it is necessary to inspect the blades of the turboshaft engine in order to detect any defects such as cracks or splits. A turboshaft engine blade includes a superalloy structural body covered with a plurality of layers of material in order to form the coating of the blade. During its use the coating of the blade wears and is eaten away and must be replaced in order to ensure optimal operation of the blades. The replacement of the coating of a blade necessitates on the one hand removing the worn coating and on the other hand applying a new coating to the body of the blade.
In practice, following the removal of the worn coating the blade is inspected in order to detect possible defects such as cracks or splits in the body of the blade. This makes it possible to avoid a situation in which a blade of which the superalloy body has been damaged is coated with a new coating.
It is known that a blade coating generally includes at least one metal layer covering the body of the blade and a ceramic layer covering the metal layer. In the course of its operation, the coating may develop oxides and may exhibit portions which are corroded or polluted (dirt, grease, combustion residues, etc.). The metal layer of which the thickness is between 50 and 100 μm is conventionally designated “metal sub-layer” by the person skilled in the art whilst the ceramic layer of which the thickness is between 150 and 350 μm is conventionally designated “thermal barrier”. Such a coating is known from the application FR 2814473 A1 in the name of Snecma.
The method of removal of the worn coating of the blade includes a plurality of successive steps such as steps of stripping, sanding and cleaning by means of jets of water and/or immersion in acid baths. A method according to the prior art results in emissions of dangerous substances into the atmosphere and into water, which present a drawback for the environment. Moreover. such a method is long taking into account the various steps which must be implemented consecutively.
In fact, as an example, in order to remove a coating from a turboshaft engine blade the following steps are implemented:                cleaning of the surface of the blade in a non-aggressive manner in order to remove all the oxides and pollutants present on the surface of the blade;        inspection of the cleaned surface of the blade in order to determine whether the blade can be repaired; and        cleaning of the surface of the blade in an aggressive manner in order to remove the different layers of the coating of the blade;        
The cleaning referred to as “non-aggressive” includes steps of degreasing of the blade, cleaning of the internal circuits of the blade and removal of the surface oxides.
The cleaning referred to as “aggressive” includes, for its part, steps of sanding of the blade, stripping of the thermal barrier, stripping of the metal sub-layer and other layers, cleaning of the surfaces and splits in the superalloy blade body, and cleaning of the cooling channels of the blade.
After repair of the body of the blade, a step of sanding is conventionally implemented in order to give the body of the blade a roughness which favours the adhesion of a coating.
The different cleaning actions previously cited are generally implemented manually and produce heterogeneous results depending upon the operators, in particular during the sanding. In certain cases, the superalloy blade body can sometimes be damaged during the cleaning and the blade must be scrapped. Furthermore, such a method can last for several hours, which presents a drawback.